Sheet feeding apparatus

ABSTRACT

A sheet feeding apparatus in which a stack of sheets is supported on a movable base plate. The base plate is adapted to move successive uppermost sheets into engagement with a feed roller. A retard roller contacts the feed roller to define a nip therebetween. In this manner, the feed roller contacts the uppermost sheet of the stack as well as the retard roller so as to advance the sheet into the nip defined therebetween preventing multiple sheet feeding.

United States Patent 1191 Kraft 1 Jan. 21, 1975 SHEET FEEDING APPARATUS 3,260,521 7/1966 Moxness 271/127 x [75] Inventor: William A. Kraft, Pittsford, N.Y. I

'Primary Examiner-R1chard A. Schacher Asslgneei Xerox Corporation, Stamford, Assistant Examiner-Bruce H. Stoner, Jr.

Conn- Attorney, Agent, or FirmH. Fleischer; C. A. Green; 22 Filed: Nov. 6, 1972 Ralabat? [21] Appl. No.1 304,032 [57] ABSTRACT A sheet feeding apparatus in which a stack of sheets is [22] 27l/1226257h1/3l; Supported on a movable base plate The base plate is i 121 127 adapted to move successive uppermost sheets into en- 1 0 earc "5 gagement with a feed roller. A retard roller contacts the feed roller to define a nip therebetween. In this manner, the feed roller contacts the uppermost sheet [56] References Cited of the stack as well as the retard roller so as to ad- UNITED STATES PATENTS vance the sheet into the nip defined therebetween pre- 2,359,856 10/1944 Morse 271/125 venting multiple sheet feeding. 3,047,290 7/1962 Thomsen 3,210,073 10/1965 Godlewski 271 125 4 Claims, 3 Drawlng Figures SHEET FEEDING APPARATUS The foregoing abstract is neither intended to define the invention disclosed in the specification, nor is it intended to be limiting as to the scope of the invention in any way.

BACKGROUND OF THE INVENTION This invention relates generally to an electrophotographic printing machine, and more particularly concerns an apparatus arranged to cause a single sheet to be separated and advanced from a stack of sheets.

Conventional electrophotographic printing machines have mechanisms therein for supporting a stack of sheets and for advancing single sheets in seriatim therefrom. It is well known that the separation and seriatim feeding of sheets from a stack or pile of sheets presents many problems due to the differences in the size, weight, stiffness and surface characteristics of the sheet material. Moreover, the characteristics of the sheets will vary depending upon humidity and electrostatic conditions.

Various types of sheet feeding systems have heretofore been utilized in electrophotographic printing machines. One such system utilizes feed rollers mounted pivotably and biased into engagement with the uppermost sheet of the stack. The feed rollers cooperate with drag pads engaging the side edge of the stack to insure that only single sheets are fed from the stack. This technique depends upon each sheet in the stack being relatively flush with one another on both sides thereof. The retarding force provided by the drag pads must be greater than the force binding successive sheets, and the sheets must have sufficient beam strength to resist bowing from the retarding force. Another system utilizes feed rollers pivoted into engagement with the uppermost sheet of a stack and snubbers securing the leading edge of the stack. This type of system frequently utilizes a reverse buckle to bring the sheet out from beneath the snubbers, and subsequent forward feeding thereof. The foregoing design depends upon sheet stiffness and the alignment of the sheets in the sheet tray. Both the drag pad approach and the snubber approach depend upon sheet beam strength. Another technique employed frequently utilizes vacuum feed arms operating in conjunction with an elevating sheet tray to pick up the top sheet from the stack and advances it into a set of feed rollers. Alternately, an adhesive on a rotating roll may pick up the uppermost sheet and advance it into the set of feed rollers. In this type of system the vacuum or adhesive will separate the sheets only as long as the binding force between successive sheets is less than the weight of the second sheet. Another approach heretofore attempted is to use a feed roller mounted stationarily within the sheet feeding apparatus and engaging or spaced from a knife edge. The tray housing the stack of sheet material is pivoted such that the uppermost sheet therein engages the stationary feed roller and is advanced over the knife edge. However, should the paper curve or bend in a downwardly direction, the sheet may jam on the knife edge preventing the feeding thereof. Still another system utilizes a stationary feed roller cooperating with a retard roller biased into engagement therewith or spaced therefrom, and a nudger roller or endless belt that is biased against the uppermost sheet of the stack. The nudger roller or belt advances the uppermost sheet into a nip defined by the retard roller and feed roller which prevents multiple sheet feeding. This method depends upon the friction between the retard roller and sheets being greater than the bonding force between two successive sheets. However, the retard roller frequently mars or notches the sheets, particularly if the approach angle to the feed nip is not consistent. In addition, retard roller wear is excessive when the roller is an abrasive material. It is, therefore, apparent that numerous approaches have been attempted in order to reliably separate and seriatim feed sheets from a stack thereof. However, each of the methods heretofore utilized includes one or more limitations which do not enhance their desirability.

Accordingly, it is a primary object of the present invention to improve a sheet feeding apparatus utilized in an electrophotographic printing machine whereby the uppermost sheet is separated from the remaining sheets of the stack and advanced therefrom.

SUMMARY OF THE INVENTION Briefly stated, and in accordance with the present invention, there is provided an apparatus for separating and advancing successive sheets in seriatim, from a stack of sheets.

In the present instance, the preferred embodiment of the apparatus includes a shaft member, a retard roller mounted eccentrically on the shaft member, and a rotary driven feed roller. The retard roller is adapted to be pivoted from an inoperative position spaced from the advancing sheet to an operative position in engagement therewith. Prior to the advancement of the sheet from the stack, the feed roller engages the retard roller and the sheet to be advanced therefrom. As the feed roller rotates, the sheet is advanced into the nip defined by the feed roller and retard roller. In this manner, the retard roller' cooperates with the feed roller to permit only a single sheet to be interposed therebetween preventing multiple sheet feeding.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which:

FIG. 1 depicts schematically an electrophotographic printing machine having the sheet feeding apparatus of the present invention included therein; and

FIG. 2 is an enlarged perspective view illustrating the FIG. 1 sheet feeding apparatus.

FIG. 3 is an enlarged perspective view depicting the relationship between the feed roller, retard roller and stack of sheets in the FIG. Zsheet feeding apparatus.

While the present invention will be described in connection with a preferred embodiment thereof, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF INVENTION A general understanding of an electrophotographic printing machine, in which the present invention may be incorporated, is bad by referring to FIG. 1. FIG. I schematically illustrates the various components of an electrophotographic printing machine adapted to produce multi-color copies from a colored original. Continued reference will hereinafter be made to the drawings wherein like reference numerals have been used throughout to designate like elements.

The printing machine depicted in FIG. 1 utilizes a photoconductive member having a drum with a photoconductive surface 12 thereon. Basically, drum 10 is mounted rotatably within the frame (not shown) of the printing machine and is adapted to rotate in the direction of arrow 14. In this manner, drum 10 moves photoconductive surface 12 sequentially through a series of processing stations A through E, inclusive. These stations will be hereinafter described briefly.

Initially, drum 10 rotates in the direction of arrow 14 to move photoconductive surface through charging station A. A corona generating device, indicated generally at 16, is positioned at charging station A. Corona generating device 16 extends in a generally transverse direction across photoconductive surface 12. In operation, corona generating device 16 charges photoconductive surface 12 to a relatively high substantially uniform potential. For example, a corona generating device of the type described in U.S. Pat. No. 2,778,946 issued to Mayo in 1957 may be suitable for utilization in the electrophotographic printing machine of FIG. 1.

Thereafter, drum 10 is rotated to exposure station B where a charged photoconductive surface 12 is exposed to a colored filtered light image of the original document. A moving lens system, generally designated by the reference numeral 18, and a color filter mechanism, shown generally at 20, are disposed at exposure station B. U.S. Pat. No. 3,062,108 issued to Mayo in 1962 is one type of moving lens system suitable for use in the foregoing electrophotographic printing machine. As illustrated in FIG. 1, original document 22 is supported stationarily face down upon transparent viewing platen 24. Successive incremental areas of original 22 are scanned by lamp assembly 26 and lens system 18 moving in a timed relation with drum 10. This scanning process produces a flowing light image of original 22 on photoconductive surface 12. During exposure, filter mechanism interposes selected colored filters into the optical light path of lens 18. Each filter operates on the light rays passing through the lens to record an electrostatic latent image on photoconductive surface 12 corresponding to a preselected spectral region of the electromagnetic wave spectrum, hereinafter referred to as a color separated latent image.

After the electrostatic latent image is recorded on photoconductive surface 12, drum 10 rotates to development station C. At development station C, there are located three individual developer units, generally designated by the reference numerals 28, 30 and 32, respectively. Each of the foregoing developer units is of the type described in copending application Ser. No. 255,259, filed in 1972. As disclosed therein, developer units 28, 30 and 32, respectively are all magnetic brush systems. A typical magnetic brush system uses a magnetizable developer mix having carrier granules and toner particles therein. The developer mix is continually brought through a directional flux field to form a brush thereof. Development is achieved by bringing the electrostatic latent image recorded on photoconductive surface 12 into contact with the brush of developer mix. Each of the respective developer units, i.e., 28, 30 and 32, contain discretely colored toner particles corresponding to the complement of the spectral region of the wavelength of light transmitted through filter 20. For example, a green filtered electrostatic latent image is rendered visible by depositing green absorbing magenta toner particles thereon. Similarly, blue and red electrostatic latent images are developed with yellow and cyan toner particles, respectively.

Once the color separated electrostatic latent image is developed, drum 10 rotates to transfer station D where the single color powder image adhering electrostatically to photoconductive surface 12 is transferred to a sheet of final support material 34. Suitable final support material may be plain paper, thermoplastic sheets, amongst others. A bias transfer roll, shown generally at 36, recirculates support material 34 and is electrically biased to a potential of sufficient magnitude and polarity to electrostatically attract toner particles from photoconductive surface 12 to sheet 34. U.S. Pat. No. 3,612,677 issued to Langdon in 1971 describes a suitable electrically biased transfer roll. Transfer roll 36 rotates in synchronism with drum 10 so that sheet 34 secured releasably thereon is moved, in registration with the powder image on photoconductive surface 12, into the nip between drum 10 and roller 36. Sheet 34 is secured to transfer roll 36 and moves in a recirculating path therewith enabling successive toner powder images to be transferred thereto, in superimposed registration, from photoconductive surface 12. In this way, a multi-layered toner powder image is formed on sheet 34 corresponding in color to the original multi-colored document. Sheet 34 is advanced from stack 38 housed in the sheet feeding apparatus, indicated generally by the reference numeral 40, of the present invention. Sheet feeding apparatus 40 will be hereinafter discussed in detail. The advancing sheet moves between a pair of baffles 42 and is directed into the nip of register rollers 44. Register rollers 44 align and forward sheet 34 to gripper fingers 46 of tranfer roll 36. Gripper fingers 46 secure releasably thereto sheet 34 for movement in a recirculating path on transfer roll 36.

After a plurality of toner powder images have been transferred to sheet 34, gripper fingers 46 release sheet 34 and stripper bar 48 separates sheet 34 from transfer roll 36. Sheet 34 is stripped from transfer roll 36 and transported on endless belt conveyor 50 to fixing station E where a fuser, indicated generally at 52, coalesces the transferred powder images to sheet 34. One type of suitable fuser is described in U.S. Pat. No. 3,498,592 issued to Moser et al. in 1970. After the fusing process, sheet 34 is advanced by endless belt conveyors 54 and 56 to catch tray 58 for subsequent removal therefrom by the machine operator.

Although a preponderance of the toner material is transferred to sheet 34, invariably some residual toner particles remain on photoconductive surface 12 after the transfer thereof to sheet 34. The residual toner is removed from drum 10 as it moves through cleaning station F. Here the residual toner is first brought under the influence of a cleaning corotron (not shown) adapted to neutralize the electrostatic charge remaining thereon. The neutralized toner is then mechanically cleaned from photoconductive surface 12 by rotatably mounted fibrous brush 60. A suitable brush cleaning device is described in U.S. Pat. No. 3,590,412 issued to Gerbasi in 1971. Rotatably mounted brush 60 is positioned at cleaning station F and maintained in contact with photoconductive surface 12. In this manner, residual toner particles remaining on photoconductive surface 12 after each transfer operation are removed therefrom.

It is believed that the foregoing description is sufficient for purposes of the present application to illustrate the general operation of an electrophotographic printing machine embodying the teachings of the present invention therein. Referring now to the specific subject matter of the present invention, illustrated in detail in FIG. 2, the sheet feeding apparatus will be discussed hereinafter. Turning once again to FIG. 1, feed roller 62 in operative communication with retard roller 64 separates and advances the uppermost sheet 66 from stack 38. Uppermost sheet 66 advances in the direction of arrow 68 into baffle 42 so as to be processed in the manner heretofore described.

Referring now to FIG. 2, sheet feeding apparatus 40 is depicted therein in detail. Sheet feeding apparatus 40 includes a sheet tray, indicated by the reference numeral 70 mounted pivotably on frame member 72 secured fixedly to the printing machine. As depicted in FIG. 2, sheet tray 70 pivots in a clockwise direction so that the leading marginal edge portion of uppermost sheet 66 engages feed roller 62. A pair of springs (not shown) suitably mounted to sheet tray 70 resiliently urge sheet tray 70 to pivot in the clockwise direction. Sheet tray 70 includes a base plate 74 having a generally planar surface for supporting stack 38 thereon. Stack 38 is positioned both longitudinally and laterally on base plate 74 by means of margin guides 76 and 78. Margin guide 78 is mounted fixedly to base plate 74, while margin guide 76 is mounted slidably thereon. Margin guide 76 is adapted to move in the direction indicated by arrow 80 so as to be adjustable for accommodating various stack widths thereon. Base plate 74 includes a plurality of longitudinally extending slots 82, 84, and 86. Rear guide 88 is mounted slidably on base plate 74 in slots 82, 84, and 86, respectively. A suitable clamp or fastener (not shown) frictionally secures rear guide 88 in the desired position. In this way, rear guide 88 is adapted to slide, in the direction of arrow 90, relative to base plate 74 so as to be adjustable length wise for any size stack supported thereon. Margin guide 76 is also secured in a slot (not shown) transverse to slots 82, 84, and 86 on base plate 74 by suitable means, e.g., a clamp or screw engaging base plate 74. This permits margin guide 76 to move slidably relative to base plate 74. By way of example, base plate 74 can accommodate support material varying in width from 8 to 8 /2 inches and in length from to 14 inches. Margin guides 76 and 78 have a generally vertical planar surface for aligning the side edge portions of a stack of sheet material disposed on base plate 74. Similarly, rear guide 88 includes a generally vertical planar surface for aligning the trailing edge portion of the stack of sheet material disposed on base plate 74. Feed roller 62 is driven by a suitable motor (not shown) in the direction of arrow 92 so as to advance the uppermost sheet 66 in the direction of arrow 68. Shaft 94 secures feed roller 62 fixedly to the printing machine. In this way, feed roller 62 is, preferably, arranged only to rotate in the direction of arrow 92 and does not articulate in any manner but remains stationary and the uppermost sheet of the stack is brought into engagement therewith. Feed roller 62 has a first portion 96 of the circumferential surface thereof engaging retard roller 64, and a second portion 98 of the circumferential surface thereof engaging sheet 66. As positioned, feed roller 62 has first portion 96 engaging retard roller 64 substantially simultaneously with second portion 98 engaging sheet 66. Retard roller 64 is mounted eccentrically on shaft 100. Shaft 100 is mounted rotatably within the printing machine frame and is adapted to pivot retard roller 64 from a first position spaced from feed roller 62 to a position in engagement therewith.

With continued reference to FIG. 2, there is shown sheet 66 being advanced by feed roller 62 cooperating with retard roller 64. As shown therein, retard roller 64 is in engagement with feed roller 62. The foregoing is achieved by biasing means or spring 102 pivoting handle 104 in direction of arrow 106. Handle 104 is secured to one end portion of shaft 100. In this way, retard roll 64 is pivoted into engagement with feed roller 62. Spring 102 is secured in notch 99 in handle 104 and attached fixedly to frame 72 via pin 101. Preferably, spring 102 has 36 coils and an initial tension of 0 lbs. with an outer diameter of 0.190 inches, each spring wire having a thickness of 0.016 inches. Handle 108 is secured to the other end portion of shaft 100, and adapted to be manually moved in the direction of arrow 110 to disengage retard roller 64 from feed roller 94.

Turning now to FIG. 3, the cooperation between feed roller 62, retard roller 64 and sheet 66 is depicted thereat. As shown therein a first portion 96 of the circumferential surface of feed roller 62 engages retard roller 64, and second portion 98 of the circumferential surface thereof engages sheet 66. Hence, first portion 96 engages retard roller 64 substantially simultaneously with second portion 98 engaging sheet 66. In this manner, successive uppermost sheets 66 are advanced by feed roller 62 into the nip defined by retard roller 64 and feed roller 62, thereby preventing multiple sheet feeding.

In recapitulation, feed roller 62 engages retard roller 64 and the uppermost sheet 66 of stack 38. As feed roller 62 rotates in the direction of arrow 92 it advances sheet 66 in the direction of arrow 68. Advancing sheet 66 moves into the nip defined by retard roller 64 and feed roller 62. In the event that more than one sheet is being advanced, retard roller 64 will prevent passage of all but the uppermost sheet therebetween. By way of example, feed roller 62 and retard roller 64 may be made from a suitable elastomer such as natural rubber or urethane. Retard roller 64 may be configured in the shape of a horse shoe rather than a cylinder. The force of engagement between feed rollers 62 and retard roller 64 is perferably about 4.9 lbs., but may range from about 2.4 lbs. to about 7.3 lbs.

From the foregoing, it is apparent that the sheet feeding apparatus of the present invention facilitates the separation and advancement of successive uppermost sheets from a stack of sheet material disposed therein. The retard roller is mounted eccentrically on the shaft and biased into engagement with the feed roller so as to compensate for wear and insure seriatim feeding of successive single sheets. In addition, the feed roller is oversized to grip the leading marginal edge portion of 'various size sheets. Furthermore, the apparatus is designed such that the stack of sheet material engages the feed roller with a substantially constant pressure. This is achieved by the utilization of an extension spring system having a constantly decreasing pivoting force on the base plate as sheets are fed therefrom.

Thus, it is apparent that there has been provided, in accordance with this invention, an apparatus for preventing multiple feeding of sheets from a stack that fully satisfies the objects, aims and advantages set forth above. While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and broad scope of the appended claims.

What is claimed is:

1. A sheet feeding apparatus, including:

a frame member;

a base plate mounted pivotably on said frame member, said base plate having a generally planar surface for supporting thereon a stack of sheet material;

a rotatable shaft member mounted substantially fixedly on said frame member;

a retard roller mounted substantially fixedly on said shaft member, said retard roller being mounted eccentrically on said shaft member so that rotation of said shaft member pivots said retard roller from an inoperative position spaced from one surface of an advancing sheet to an operative position in contact therewith;

a rotary driven feed roller having a first portion of the circumferential surface thereof engaging the other surface of the sheet of support material and a second portion of the circumferential surface thereof engaging the circumferential surface of said retard roller disposed in the operative position thereof prior to the advancing sheet being interposed therebetween, said feed roller being adapted to advance the sheet into the nip defined by said feed roller and said retard roller to prevent multiple sheet feeding;

means for supporting substantially fixedly said rotary driven feed roller;

means for pivoting said base plate in an upwardly direction so that the leading edge of successive uppermost sheets of the stack supported thereon engage tangentially said feed roller, said base plate with the stack supported thereon forming an inclined surface with the leading edge of successive uppermost sheets located at a level above the trailing edge thereof;

a pair of opposed, spaced side guide means, each of said pair of side guide means having a generally planar, substantially vertical surface adapted to contact opposed side edge portions of the stack. one of said side guide means being mounted substantially fixedly on said base plate and the other of said side guide means being mounted movably on said base plate so as to engage and substantially align the side edges of-the stack mounted on said base plate and interposed therebetween; and

rear guide means mounted movably on said base plate, said rear guide means having a generally planar, substantially vertical surface disposed substantially normal to the vertical surfaces of said pair of side guide means and adapted to contact the trailing edge of the stack so as to align and locate the leading edge thereof in position to engage said feed roller when said base plate pivots in an upwardly direction.

2. An apparatus as recited in claim 2, further including biasing means for resiliently urging said retard roller to pivot from the inoperative position to the operative position in engagement with said feed roller prior to the advancing sheet being interposed therebetween.

3. An apparatus as recited in claim 2, wherein said retard roller and said feed roller are made preferably from an elastomeric material.

4. A sheet feeding apparatus as recited in claim 2, wherein said biasing means urges said retard roller into engagement with said feed roller with a force ranging from about 2.4 lbs. to about 7.3 lbs. 

1. A sheet feeding apparatus, including: a frame member; a base plate mounted pivotably on said frame member, said base plate having a generally planar surface for supporting thereon a stack of sheet material; a rotatable shaft member mounted substantially fixedly on said frame member; a retard roller mounted substantially fixedly on said shaft member, said retard roller being mounted eccentrically on said shaft member so that rotation of said shaft member pivots said retard roller from an inoperative position spaced from one surface of an advancing sheet to an operative position in contact therewith; a rotary driven feed roller having a first portion of the circumferential surface thereof engaging the other surface of the sheet of support material and a second portion of the circumferential surface thereof engaging the circumferential surface of said retard roller disposed in the operative position thereof prior to the advancing sheet being interposed therebetween, said feed roller being adapted to advance the sheet into the nip defined by said feed roller and said retard roller to prevent multiple sheet feeding; means for supporting substantially fixedly said rotary driven feed roller; means for pivoting said base plate in an upwardly direction so that the leading edge of successive uppermost sheets of the stack supported thereon engage tangentially said feed roller, said base plate with the stack supported thereon forming an inclined surface with the leading edge of successive uppermost sheets located at a level above the trailing edge thereof; a pair of opposed, spaced side guide means, each of said pair of side guide means having a generally planar, substantially vertical surface adapted to contact opposed side edge portions of the stack, one of said side guide means being mounted substantially fixedly on said base plate and the other of said side guide means being mounted movably on said base plate so as to engage and substantially align the side edges of the stack mounted on said base plate and interposed therebetween; and rear guide means mounted movably on said base plate, said rear guide means having a generally planar, substantially vertical surface disposed substantially normal to the vertical surfaces of said pair of side guide means and adapted to contact the trailing edge of the stack so as to align and locate the leading edge thereof in position to engage said feed roller when said base plate pivots in an upwardly direction.
 2. An apparatus as recited in claim 2, further including biasing means for resiliently urging said retard roller to pivot from the inoperative position to the operative position in engagement with said feed roller prior to the advancing sheet being interposed therebetween.
 3. An apparatus as recited in claim 2, wherein said retard roller and said feed roller are made preferably from an elastomeric material.
 4. A sheet feeding apparatus as recited in claim 2, wherein said biasing means urges said retard roller into engagement with said feed roller with a force ranging from about 2.4 lbs. to about 7.3 lbs. 